DiskGallery

A read-only macOS app that catalogs external drives so their contents stay browsable while disconnected — a "GPS for digital archives." Plug in a backup drive, scan it once, and DiskGallery records every file and folder with its size. Keep all your drives mapped in one place to compare them, find duplicate copies across backups, and mark what to keep vs delete.

Cataloging is strictly read-only — scanning and hashing never modify your drives (enforced by MutationGuardTests). The only thing DiskGallery writes to a drive is the Finder tags you explicitly apply; everything else lives in its own local catalog database.

Features

• Library of drives — each identified by volume UUID, with live connected / disconnected badges.
• Instant offline browsing — Finder-like tree with folder sizes pre-computed and stored, so it's fast even with the drive unplugged. Single-click selects (⌘/⇧ for multi-select); double-click opens a folder.
• Duplicate finder — groups files by name + size across all drives (works offline), with an optional on-demand SHA-256 "verify by content" when a drive is connected, plus reclaimable-space totals.
• Two tag dimensions — a Keep / Delete / Review decision and a Finder color (the 7 standard colors). Decisions survive re-scans; both are written to the file as real macOS Finder tags when the drive is connected, so they show up in Finder too.
• Keyboard tagging — Q/W/E for Keep/Delete/Review, 1–7 for colors, all rebindable in Settings. Acts on the whole multi-selection at once.
• Themes — six accent colors and light / dark / system mode, all in Settings.
• Full-text name search across every cataloged drive.

Install

Grab the latest signed .dmg from the Releases page and drag DiskGallery to Applications. The app checks for updates itself (Sparkle); you can also pick DiskGallery → Check for Updates… at any time.

Requirements

• macOS 15+, Xcode 26 / Swift 6.

Build & run

# Generate the Xcode project (only needed after editing project.yml; the .xcodeproj
# is committed, so you can also just open it directly).
xcodegen generate            # brew install xcodegen

# Build
xcodebuild -project DiskGallery.xcodeproj -scheme DiskGallery \
  -configuration Debug -destination 'platform=macOS,arch=arm64' build

# Run the tests
xcodebuild -project DiskGallery.xcodeproj -scheme DiskGalleryCore \
  -configuration Debug -destination 'platform=macOS,arch=arm64' test

Or open DiskGallery.xcodeproj in Xcode and press Run. In the app, click Scan… and choose a drive (or any folder) to catalog.

Headless scan

DiskGallery.app/Contents/MacOS/DiskGallery --scan /Volumes/YourDrive

Scans into the default catalog and exits — handy for scripting.

Architecture

• DiskGalleryCore (framework) — all logic, fully encapsulating GRDB/SQLite:
  • Scanning/ — read-only directory enumeration, batched inserts, O(n) folder-size rollup, progress + cancellation.
  • Data/ — GRDB models, schema migrations, WAL-tuned database.
  • Duplicates/, Annotations/, Search/, Library/ — the query engines.
  • Catalog — the single public facade the app talks to.
• DiskGallery (app) — SwiftUI; imports only DiskGalleryCore (never GRDB). Three-column NavigationSplitView: drives sidebar, tree browser, detail + tag editor. VolumeService tracks mounts via NSWorkspace.

The catalog lives at ~/Library/Application Support/DiskGallery/catalog.sqlite.

Known v1 limitation

Duplicate "verify by content" resolves a file as volumeMount + relativePath, which is correct when a drive was scanned from its volume root (the normal case). Scanning a sub-folder instead of the whole drive can make hash verification unable to locate files; browsing, duplicate detection, and tagging are unaffected.

License

Released under the MIT License. © 2026 Mr. Barkan.